During Howard Stern's radio show on Sept. 9, Robin Quivers revealed that she had been fighting cancer during her yearlong absence from the studioCredit: Steve Mack/FilmMagic

Howard Stern's Sirius XM radio show is never short on shock value, but even longtime listeners were surprised by the Monday, Sept. 9, broadcast. During an uncharacteristically emotional segment on the show, Stern's sidekick, Robin Quivers, revealed that she had been fighting cancer for the last year.

Quivers, 61, had been absent from the studio since mid-2012 (but broadcasting from home for most of that time) -- and now fans know why. Speaking about her recent health scare with Stern, she explained that the cancer had been discovered in the endometrial tissue in her uterus about a year ago. Since then, she has undergone successful surgery, radiation, and chemotherapy; doctors believe she is now in remission.

The initial prognosis was scary, though. As Quivers told listeners, it took 12 hours for surgeons to remove the grapefruit-sized tumor last May. "It was so huge that it was lying on all the organs in my pelvis, and they literally had to scrape it off when they got to it," she explained. "They couldn't even figure out how to operate at one point because it was so massive."

Listening to his right-hand woman tell her story on Monday, Stern recalled his initial reaction to the diagnosis. "I gotta be honest, I thought she was a goner," he confessed.

In fact, he was preparing himself for her death. "I'll tell you how serious this was: I was already making funeral arrangements," he said. "Not to make light of this situation -- I didn't know what was going on. I was freaking out."

Had she been unable to return, it would have been the end of Stern's show. "Doing a show without Robin is like cutting off my left arm. Or my right arm. Or maybe both," he said during the first broadcast without Quivers last year.

"She was my backbone, you understand," he explained. "Where I would lose courage, Robin always had the courage. She always is the brave one. Always the brave one with me. I could go to her, and I could always rely on her."

In fact, when she announced she was having a "procedure" done on her bladder last May, he told her: "I'll f--king kill you if you have cancer. I'm not doing the show without you...I'm quitting if you're not doing the show."